Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
A cellular wireless network may include a number of base stations that radiate to define wireless coverage areas, such as cells and cell sectors, in which user equipment devices (UEs) (also known as wireless communication devices (WCDs)) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the network may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
In general, a cellular wireless network may operate in accordance with a particular air interface protocol or “radio access technology,” with communications from the base stations to UEs defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) or Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for Mobile Communications (GSM), among others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handoff between coverage areas, and functions related to air interface communication.
In accordance with the air interface protocol, each coverage area may operate on one or more carrier frequencies or blocks of frequencies (e.g., frequency bands, such as 698-960 MHz, 1610-2025 MHz, etc.) and may define a number of air interface channels for carrying information between the base station and UEs. These channels may be defined in various ways, such as through frequency division multiplexing, time division multiplexing, and/or code-division multiplexing, for instance. By way of example, each coverage area may define a pilot channel, reference channel or other resource on which the base station may broadcast a pilot signal, reference signal, or the like that UEs may detect as an indication of coverage and may measure to evaluate coverage strength. As another example, each coverage area may define one or more uplink control channels or other resources on which UEs may transmit control messages to the base station. And each coverage area may define one or more downlink control channels or other resources on which the base station may transmit control messages or other information to UEs. Each coverage area may then define one or more traffic channels or other resource for carrying communication traffic such as voice data and other data between the base station and UEs.
When a UE first powers on or enters into coverage of the network and seeks to connect to a coverage area of the network, the UE may scan the pilot or reference signals of the network's coverage areas in an effort to determine a signal strength of each respective pilot or reference signal. The UE may then identify, for example, a coverage area with a strongest pilot or reference signal (e.g., having the highest signal-to-noise ratio) and may register with that coverage area by transmitting a registration request or attach request to a base station providing that signal and serving that coverage area. This registration process may serve to notify the network of the UE's presence in a particular coverage area and to facilitate network authentication of the UE. Once registered, the UE may then operate in an idle mode (i.e., the UE may idle in the selected coverage area) in which the UE monitors a downlink control channel to receive overhead information and to check for any page messages. In the idle mode, the UE may have no assigned traffic channel resources on which to engage in bearer communication.
Further, when the UE is operating in the idle mode, the UE may continue to regularly scan pilot or reference signals, from both the coverage area in which the UE is idling and any other coverage areas that extend to the UE's location, to help ensure that the UE continues to operate in the coverage area providing the strongest coverage. Through this process, if the UE thereby detects that another coverage area is stronger than the coverage area in which the UE is idling, the UE may then transition to idle in that other coverage area instead (i.e., the UE may engage in idle handoff to the other coverage area).